The present invention relates to high-strength, liquid formulations of N-phosphonomethyl glycine (glyphosate), more particularly, the monomethylamine (MMA) and the dimethylamine (DMA) salts of glyphosate.
Glyphosate is a known, effective herbicide. U.S. Pat. No. 4,405,531 discloses a long list of organic ammonium salts of glyphosate useful as herbicides, including the methylamine salt and dimethylamine salt, and, as an example, monoalkylammonium and dialkylammonium are listed as a particularly preferred salts. Various formulations are currently marketed, many of which are aqueous solutions that can be used as is or diluted prior to use. Typically the glyphosate is provided as a salt, which exhibits sufficiently high solubility in water to provide a high-strength herbicidal formulation. For example, U.S. Pat. No. 6,277,788 discloses both the isopropylamine salt (IPA) and the monoethanolamine (MEA) salt of glyphosate. Additionally, U.S. Pat. No. 6,365,551 and WO 01/89302 disclose various formulations that include the potassium (K) salt of glyphosate. A high-strength formulation is desirable for a variety of economic and environmental reasons. For example, it is desirable to provide a high-strength formulation to reduce shipping and handling costs and to reduce the amount of packaging material that must be disposed. The high-strength formulations should be stable and retain potency during storage and shipping. Furthermore, the high-strength formulation should be a clear, homogeneous liquid that is stable at temperatures at least as high as 50° C. and should not exhibit any precipitation at temperatures as low as 0° C.
The herbicidal formulations typically include an efficacy-enhancing surfactant. Inclusion of a surfactant is highly desirable because the resulting formulation exhibits a substantially increased herbicidal activity. WO 03/063589, for example, describes glyphosate formulations using alkylbetaine surfactants in combination with other surfactants. However, selected surfactants either can interact with the glyphosate salt, increasing the viscosity of the herbicidal formulation, or are generally incompatible with the glyphosate salt solution. Certain surfactants, for example, some of the surfactants in the oxyalkylene alkylamine class of compounds, when combined with the glyphosate salt, increase the viscosity of the formulation. If the viscosity is too high, handling of the concentrated herbicide can be difficult. Furthermore, highly viscous liquids are difficult to accurately measure, either for application to the plants or for dilution to a less concentrated spray solution. Depending upon the concentration and specific surfactant, the herbicidal formulation can form a gel, which makes most applications extremely difficult if not impossible to perform.
Formulations of the commonly used IPA salt of glyphosate become increasingly viscous at concentrations greater than 350 gram acid equivalent per liter (gae/l), particularly at concentrations greater than 440 gae/l. The high viscosity makes the formulation difficult to measure and pump, especially at the lower temperatures typically encountered at the beginning of the season.
A major limitation of the MEA and K salts of glyphosate is the incompatibility with a wide range of surfactants. In particular, U.S. Pat. No. 6,277,788 discloses that polyoxyethylene alkylamines are only compatible with the MEA salt of glyphosate when the sum of the total average number of carbon atoms plus the average number of oxyethylene groups is equal to or less than 25. Although the K salt of glyphosate offers the ability to form low viscosity, high strength glyphosate formulations, it has some significant limitations in that many surfactants commonly used to enhance the efficacy of glyphosate are not compatible with the glyphosate K salt solution. For example, commonly used alkylamine ethoxylate surfactants are only compatible (form a homogeneous mixture) when the degree of ethoxylation is no more than about 5. Alkylamine ethoxylate surfactants with low degree of ethoxylation have a higher potential to cause eye irritation, however, than alkylamine ethoxylate surfactants with a higher degree of ethoxylation, e.g. 15-20 mole ethylene oxide.
In light of the above described problems, there is a continuing need for additional improvements in the relevant fields including improved high-strength herbicidal formulations that exhibit low viscosity and which contain a suitably efficacious surfactant. The present invention addresses these needs and provides a wide variety of benefits and advantages.